Spiraling brick arch construction for rotary kiln



SRIRALINC BRICK ARCH CONSTRUCTION FCR ROTARY KILN Filed sept. 27, 1960 Oct. 9, 1962 H. STRUCKMANN 5 Sheets-Shea?l l f INVENTOR HOLGER STRUCKMANN 02m @mmm ATTORNEYS.

Oct- 9, 1962 H. STRUCKMANN 3,057,612

SPIRALING BRICK ARCH CONSTRUCTION FOR ROTARY KILN Filed sept. 27, 1960 s sheets-sheet 2 INVENTOR HOLGER STRUCKMANN ATTORNEYS.

Oct. 9, 1962 H. sTRucKMANN 3,057,512

SPIRALING BRICK -ARCH CONSTRUCTION FOR ROTARY KILN Filed Sept. 27, 1960 5 Sheets-Sheet 5 FIG. 6. FIG. 'Z

STEEL KILN SHELL DIRECTION OF ROTATION MATERIAL HEIGHT BASED ON 8' DIAMETER INSIDE OF KILN LINING INVENTOR HOLGER STRUCKMANN ATTORNEYS.

United States Patent 3,057,612 Patented Oct. 9, 1962 ice 3,057,612 SPIRALIN G BRICK ARCH CONSTRUCTION FOR ROTARY KILN Holger Struckmann, 160 Nichols Ave., Stamford, Conn. Filed Sept. 27, 1960, Ser. No. 58,833 Claims. (Cl. 263-33) The present invention relates to internal rotary kiln constructions and more particularly to means therein to effect better fuel economy in their use.

Rotary kilns are long steel tube like structures lined with tire brick and mounted at a slight slope to the horizontal. The material to be treated is fed in at the higher end and gradually works its way down through the kiln as the kiln rotates. Fuel and air for combustion are entered at the lower end where combustion takes place. The hot combustion gases pass upwardly to the feed end and on out of the kiln through a stack. Although counter-current flow exists between the gases and the material being treated, the fuel economy is nevertheless far from good due to the poor heat transfer relationship between the material and the gases. Many different methods such as dams, baille rings, vanes and other means have been tried to eiect a better heat transfer relationship, but these for the most part are expensive to install and operate.

The primary object of the present invention is to provide a rotary kiln construction wherein better -fuel economy and increased production will result at a relatively small increase in cost when applied to a conventional rotary kiln.

Further objects of the invention are to provide in a rotary kiln construction, means which can be used (1) to propel or retard material flow through the kiln; (2) to disrupt the movement in the material bed, whereby not only the outer layers of the material bed are exposed to the gases and the kiln lining; (3) to insert into the material bed hot brick surfaces to increase the area of heat conduction; (4) to increase the degree of contact between the material and gases by dribbling material in a relatively diffused state into the outer edges of the gas stream, without placing said material in such a position that it is readily picked up and carried away by the gases, and (5) to spiral the kiln gases so that they make greater contact with all the exposed internal surfaces as well as throw outwardly centrifugally any entrapped dust in the gases.

The foregoing and other objects of the invention, not specifically enumerated, are achieved by providing in a rotary kiln, brick arches `disposed in a manner such that the plane of each arch is perpendicular to the center line of the kiln, with each arch angularly olf-set to its adjacent arch, the net effect of a combination of the arches being to spiral the hot gases of combustion so that they come in better contact with the material moving along the bottom of the kiln. Preferably these arches can be constructed so as to raise the material slightly and then let it fall in a dribble or diffused state in which it can be better contacted by the spiraling gases.

The invention will be better understood from the detailed description which follows when considered in conconnection with the accompanying drawings wherein:

FIG. l is a schematic representation of a rotary kiln showing the location therein of the spiraling arch construction embodying the present invention.

FIG. 2 is a diagrammatic section, on `an enlarged scale, through the spiraling arch construction of FIG. l, showing one complete spiral or pitch length of spiral arch, the section being taken along the line 22 of FIG. 3.

FIG. 3 is a transverse section taken along the line 3 3 of FIG. 2.

FIG. 4 is a transverse section tak-en along the line 4-4 of FIG. 2.

FIG. 5 is a schematic cross-section through a conventional rotary kiln showing the theroretical transverse movement of material being treated therein during rotation of the kiln.

FIGS. 6, 7, 8 and 9 are schematic cross-sections showing the theoretical positions of the height of material being treated in a kiln having a spiral arch construction as shown in FIGS. 2 to 4.

In FIG. 1 of the drawings there is shown a schematic representation of a rotary kiln embodying my invention wherein the material to be processed is charged into the upper or feed end 10, then passes through conventional heat exchanger 11, then through the portion of the length of the kiln 12 provided with the spiraling arch construction, then through the burning zone 13 and out through the discharge or lower end 14. Aside from the spiraling arch construction the kiln may be of conventional design and preferably the spiraling arch construction within the kiln should occupy approximately four tenths or more of the length of the kiln, although said length may be varied depending upon the axial length and curvature of the arches and the material to be processed in the kiln.

In FIGS. 2, 3 and 4 of the drawings, wherein I have shown `a specific embodiment of the invention, the reference numeral 1S indicates a kiln shell having therein a conventional kiln lining 16 and one complete spiral of brick arches 17 through 17k inclusive. Each arch projects inside the kiln and is constructed of a plurality of fire bricks which are braced in a corbeling manner. From FIG. 3 it will be noted that the spiraling effect is obtained by having the inner surface of each arch generated from an axis of construction 18 which is parallel to the kiln axis and which is spaced circumferentially in a reference cylinder, shown in FIG. 3 as a circle 19, concentric to the kiln axis and each axis of construction is disposed at a predetermined central angle about the axis of the kiln in the same direction in relation to the axis of construction of the next preceding arch. As shown in FIGS. 2 and 3 each arch is disposed ahead of the preceding one by an angular spacing of 30. The pitch of the spiraling Wall depends upon the axial width of each arch construction and the `angular spacing of the axes of construction of the arches. Thus, with 9" wide arches the pitch becomes 9l when there are l2 construction points 1S spaced 30 of the spiraling arch construction, it will be seen from FIG. 4 that, with the same unit heat transfer rate for all the bricks, the kiln shell will be heated unevenly which may result in serious stresses and possibly warping of the shell. Although various means may be resorted to .i for reducing such stresses, preferably they may be overcome by providing the spiraling arches with a high heat conductivity support which will readily transmit the heat from the arches to the kiln shell. Such support may be solid material such as iire brick shown at 17 or it may be a hollow steel casing 20 filled with a liquid or light weight solid or powdered metal 21 of high heat conductivity as shown in FIGS. 2 and 4.

From a consideration of the description and drawings thus far disclosed in connection with the direction of the kilns rotation, material to be processed can be either propelled forward toward the kiln discharge end or toward the feed end as desired. Normally, in low angle kilns it will be desirable to propel the material forward toward the discharge end. It is conceivable that a horizontal kiln could be made with the spiraling construction to propel the material to the discharge end, in which case the spiral provided by the arches would act much like a screw conveyor. Low angle kilns are seldom placed on less than or 1/2 per foot slope. With kilns 400 to 500 long this would means that the feed end of the kiln is some l2 to 16 higher than the discharge end and as the discharge end is already some or more above ground elevation, this means that the feed end supporting foundation becomes quite high and expensive to construct, especially with the tremendous loads to be carried. In a short high angle kiln the spiraling brick construction can be used to retard material llow, thereby giving it more time to be heated before descending into the hottest part of the kiln.

It will also be apparent that the spiraling arch construction can be used to disrupt the movement in the material bed where normally only the outer layers of thel material bed are exposed to the hot gases and the hot kiln lining. This will be better understood from a consideration of FIGS. 5 to 9 of the drawings wherein there is schematically illustrated the movement in a material bed where all the material particles are assumed to be of the same size. The action of the material in a conventional rotary kiln is shown in FIG. 5 wherein it will be noted that a particle of material in the path a is in position to pick up heat from the kiln lining being close to the inside surface of the kiln. Thus, there is a tendency as the kiln turns, for a particle of material in the path a to be carried to the free surface, exposed to the flame and cascaded to the bottom of the load, receiving during this cycle, maximum contact with the kiln surface, the hot gases and the arnes radiation. 'Ihe particle in the path b receives little heat from the kiln lining, being located near the center of the load. Furthermore, when it rises close to the surface it is cascaded down near the bottom of the load but it is still fairly well covered at all times by material in the path a. Hence if a particle finds itself located in the inner path b, there is nothing to force it into an outer path where it can readily pick up heat from the gases or the fire brick lining. The spiral lining construction disrupts this spiral pattern by mixing and churning the material bed. It will be seen from FIGS. 6 to 9 how this is done. FIG. 6 shows a 9 steel kiln shell with a 6 thick lining, giving an 8 diameter inside the lining. In conventional kilns, the material height of bed depths varies from say 1' 5 for an 8 I.D. kiln lining to about 2 2 for a 16 lining diameter. A 1' 5 bed depth is used here. In said FIG. 6 the kiln axis about which the arch construction rotates is at a distance of 1' 3 from the arch center. In this example a circular arch construction is shown similar to that in FIG. 2. The radius of the circular arch is 2 9". In FIG. 7 the kiln is shown as having rotated 90 counter-clockwise. The material head (M.H.) cannot be any further away from the kiln center than 2 7" for that is what it would be in a bare kiln. As we now assume that the material head has remained at 1' 5" in the circular section as represented by the xx line, the material will be raised 1 3" above its normal level. The width of each circular section is probably only 6 or 9" so that the eiect is that of trying to raise a tall column of unstable material on a narrow shelf. This of course is impossible and the material tlows away when not restrained. The flow results in a mixing and churning which permits the material bed to become uniformly heated rnuch quicker as a better heat transfer rate is obtained. This improved heat transfer rate should either enable use of a shorter kiln or a greater output to be obtained from a conventional kiln which has been converted to the spiraling arch construction. It will also be apparent from FIG. 6 that as the kiln rotates, the off center brick lining is forced into the material bed. As the depth of the material load or bed is usually not more than 1A of the inside kiln diameter, the brick construction should preferably be not higher than this as otherwise not all the brick in a given cross-sectional plane can be covered with material as the kiln rotates. With an 8 diameter inside the fire brick lining, the circumference will be about 25', of which 18 is always in position to absorb heat from the hot gases while 7 is in position to give up heat to the material bed. Unfortunately, in a conventional kiln, the layer of material with which the lining is in contact is as seen from FIG. 5 the hottest layer, so the heat transfer rate is less than if it were in contact with the inner or colder material. Accordingly, the amount of projection of a spiral lining into a kiln should be slightly less than the material depth in order for all the brick to come into position to give up and absorb heat as the kiln rotates.

Because of the spiral arch construction, as the kiln rotates the spiraling arch construction propels and therefore has a tendency to dribble material over the edges of the succeeding brick arches. Although every arch has the same cross-sectional shape, the arches are spread uniformly about the kiln circumference, each arch being angularly spaced a predetermined number of degrees behind the preceding arch. Material propulsion is achieved by having each arch lead its following arch by a uniform number of degrees. Material rides up on the flat surface of an arch until it passes the angle of repose. Cascading then takes place and the material falls back on itself. Due to the rather narrow surface available for cascading, the material tends to spread. Due to the high wall of the preceding arch, the material is forced to spread towards the following arch and a spilling or dribbling action occurs. This action takes place near the lower part of the kiln so the material is not thrown into the centerline of the gas stream. However, due to the spiraling of the gas stream there is a tendency for the dribbled material in falling to have a greater part of its area swept by the gases.

Furthermore, since each arch section is laid up perpendicular to the kiln axis each section leads the following section by a given amount. The net effect of this is to form a spiral which causes the kiln gases to spiral as they pass through the sections. Smoke chamber tests have shown that the further the indented parts of the sections project into the kiln, the more effective is their action in spiraling the gases. Ideally this indentation should range between 1/3 to 1/2 the normal internal kiln diameter. This, however, must be tempered with the desire to have the highest point of the indentation covered with material when passing through the deepest part of the material bed. Spiraling the gases makes them travel a longer path through the kiln, which means greater contact is made with the lining and with the material being treated and consequently greater opportunity is provided for transferring heat.

While I have shown and described a preferred embodiment of my invention and have explained why greater eliiciency will be obtained from a kiln embodying the spiraling arch construction, it is to be understood that the angular spacing between successive arches, their axial dimension and their internal projection into the kiln may be varied, within the range of engineering skill and the character of the material to be treated in the kiln, without departing from the spirit of the invention as hereinafter claimed.

What I claim is:

l. A kiln adapted to rotate about a longitudinal axis and comprising a cylindrical kiln shell having extending inwardly therefrom intermediate its ends, a spiraling arch construction consisting of a series of flat facially abutting arches each being perpendicular to the axis of the kiln and each arch having an inner arcuate surface of equal radius and generated from an axis of construction which is parallel to the kiln axis and which is spaced circumferentially in a reference cylinder concentric to the kiln axis and which is disposed at a predetermined central angle about the axis of the kiln in the same direction in relation to the axis of construction of the next preceding arch.

2. A kiln according to claim l, wherein each arch has the same dimensions.

3. A kiln according to claim l, wherein the spiraling effect is obtained by having the inner surface of each adA jacent arch of equal axial width and each axis of construction being spaced an equal angular distance from each preceding axis of construction.

4. A kiln according to claim l, wherein each of the abutting arches is formed of fire brick and is spaced inwardly from the kiln shell and high heat conducting material lls the spaces.

5. A kiln according to claim 4, wherein the high heat conducting material is fire brick.

6. A kiln according to claim 4, wherein the high heat conducting material is a light weight metal.

7. A kiln according to claim 4, wherein the ire brick arches are supported by a metallic casing spaced from the kiln shell.

8. A kiln according to claim 4, wherein the tire brick arches are supported in metallic casings.

9. A kiln according to claim 7, wherein the high heat conducting material is a liquid.

10. A kiln adapted to rotate about a longitudinal axis and comprising a spiral arch and shell construction consisting of a series of flat facially abutting, shell supported, arches each being perpendicular to the axis of the kiln and each having an inner arcuate surface of equal radius and generated from an axis of construction which is parallel to the kiln axis and which is spaced circumferentially in a reference cylinder concentric to the kiln axis and which is disposed at a predetermined central angle about the axis of the kiln in the same direction in relation to the axis of construction of the next preceding arch.

References Cited in the tile of this patent UNITED STATES PATENTS 727,540 Harvey May 5, 1903 2,694,565 Sainderichin Nov. 16, 1954 2,857,148 Niemitz Oct. 2l, 1958 FOREIGN PATENTS 357,389 Germany Aug. 23, 1922 

